Currently under construction, the Carlsbad Desalination Project will become the nation’s largest seawater desalination facility when it’s completed, providing an estimated one-third of all locally generated water in San Diego County.
In addition to the plant, a 10-mi. (16 km), large-diameter conveyance pipeline to the Water Authority’s Second Aqueduct in San Marcos is being constructed by Poseidon Resources, a private, investor-owned company that develops water and wastewater infrastructure.
“We’re trying to diversify our water supply,” said Frank Belock, deputy general manager of the Water Authority. Recent droughts have encouraged the Water Authority to include several optional sources for water, including conservation. Desalinated water is expected to account for 7 percent of the area’s total supply by 2020.
“Seawater desalination will provide a local, drought-proof supply of water to our semi-arid region and will improve the reliability of San Diego County’s water supply,” said Gina Molise, senior public affairs representative of the Water Authority. “Up to 70 percent of our current supplies are imported from sources hundreds of miles away. This new, drought-proof supply will reduce the region’s dependence on water from the Colorado River and the Bay-Delta that is vulnerable to droughts, natural disasters and regulatory restrictions.”
Agreements in Place
The Water Authority’s board of directors approved an innovative, 30-year Water Purchase Agreement with Poseidon in November 2012.
The agreement outlines the commercial and financial terms for production and delivery of desalinated ocean water to the Water Authority’s regional conveyance system. It also outlines the terms of the potential purchase of the plant by the Water Authority.
The Water Authority has an option to purchase the plant from Poseidon for the amount of outstanding debt in 10 years, said Belock. The arrangement removes responsibility from the Water Authority for the design, permitting, financing and construction of the plant. By transferring these risks to the private sector, the Water Authority is able to keep costs for water ratepayers low.
The Water Authority does own the pipeline outright, though. “Because it connects to ours physically and hydraulically, we need to control it,” Belock said. The arrangement also saves the Water Authority tens of millions of dollars in financing costs through lower interest rates.
For the next 30 years the Water Authority will buy water at the pre-defined price of $1,849 - $2,257 per acre-foot in 2012 dollars, depending on how much is purchased annually. The cost for desalinated seawater from the Carlsbad plant includes the water purchase price from Poseidon and the cost of the aqueduct modifications.
“It’s a ‘take or pay’ for the first 48,000 acre-feet,” Belock said. That covers the fixed costs of the project and the variable costs of water production. Water in excess of 48,000 acre-ft. may be purchased at the Water Authority’s discretion at a lower rate that reflects the variable costs of incremental water production.
While the impact on individual ratepayers will vary depending upon their local water agency, a typical household of four people can expect to pay approximately $5 to $7 per month more for water by 2016.
In development since 1998, the project was incorporated into the Water Authority’s 2003 Water Facilities Master Plan and into the 2005 and 2010 updates to the Urban Water Management Plan. The plant is being constructed on industrially zoned land adjacent to the Encina Power Station in Carlsbad.
A design-build agreement with Poseidon was approved for the design and construction of the new conveyance pipeline. The joint venture of Kiewit Infrastructure West and J.F. Shea Construction, Inc., was contracted to design and build the desalination plant and pipeline. IDE Technologies Ltd., a world leader in desalination technology and operations, will engineer the plant’s desalination process and related equipment and handle plant operations.
Capital investment costs include $537 million for the desalination plant, $159 million for the pipeline, $227 million in financing and $80 million for modifications to the Water Authority system. The Water Authority must modify its aqueduct system to incorporate the new supply of water.
A 5-mi.-long (8 km) section of Pipeline 3 will be relined to accommodate increased pressures from the desalination plant. A new pipeline interconnect will maintain water deliveries to the south while Pipeline 3 is being relined. The Twin Oaks Valley Water Treatment Plant will be modified to blend desalinated water with existing water supplies. Operation and maintenance is expected to cost $49 to $54 million annually.
The $1.003 billion construction budget is being financed via tax-exempt construction bonds. Taking advantage of favorable interest rates in 2012 allowed savings of $200 million.
Construction began in March 2013 and is expected to be complete in early 2015. The project will require a total of 26,000 cu. yds. (19,878 cu m) of concrete, 5.5 tons (5 t) of rebar and 79,000 ft. (24,079 m) of piping, from conduit to 72-in. (183 cm) feedline pipe. An average of 250 people working on site every day adds up to 316,000 worker hours.
“The pipeline is constructed primarily in public streets and passes through three cities,” Molise said. The 54-in. (137 cm) diameter welded steel pipeline will connect the ‘desal’ plant to the Water Authority’s regional aqueduct system.
Belock continued, explaining that the pipe will run under streets for most of its 10-mi. (16 km) length. “There are five locations where we will tunnel under streets using a jack and bore method.” Spoil will be stored on site for possible reuse, with the excess being sold.
To mitigate traffic issues creating by tunneling, Belock said some of the work — particularly in the high-tech business areas in Carlsbad — will be performed on nights and weekends. “We’re working to maintain access to businesses,” he added.
The pipeline project is not particularly unique in size or scope, he said. “One feature of note is that the pipe sections closest to the desal plant are nearly one inch thick to accommodate high-pressure flows from the plant to the Water Authority’s aqueduct.”
Another noteworthy aspect of the project is the use of an unusual excavator with 25-ft.-wide (7.6 m) treads capable of straddling the trenches. “It gives it more leverage,” Belock says.
The pipes come in 25-ft. (7.6 m) sections weighing from 8 tons (7.3 t) for the lower pressure pipes to 12 tons (11 t) for the higher pressure pipes. They will be lifted into place by three cranes, one of which is still being built. “All the equipment is coming from 11 different countries,” Belock said, “including 300 horse power pumps from Spain.” He explained that the equipment is rather standard, but that everyone working on the project is experienced and simply feels more comfortable working with familiar equipment.
Due to a State act that allows them to put pipe in the road, Belock said there have been few easement acquisitions to slow progress. Southern California’s mild weather has contributed to work progressing smoothly and on schedule.
When work is completed, Poseidon will be required to obtain a permit from the California Department of Public Health to deliver drinking water to the Water Authority’s aqueduct system. Belock traces the water taken from the Pacific Ocean through treatment at the seaside plant, then down the new pipeline for 5 mi. (8 km) to the authority’s treatment plant, where it will be blended with treated water before delivery to customers. “Traveling through the pipe results in chlorine residual degradation, so we’ll add more chlorine at our facility,” he said.
Once the facility begins producing water for the San Diego County region in 2016, this new supply and its cost will be melded with the Water Authority’s other water supplies serving 24 member water agencies and 3.1 million people.